The defendants, both of St Stephen's Close, Longsight, Manchester, were convicted by a jury of conspiracy to murder and conspiracy to rob after just four hours' deliberations following a three-week trial.

Judge Francis Gilbert QC, The Recorder of Exeter, told Liverpool: ``You intended to rob her and kill her and dump her body in the river, according to your words, and then leave the country with your accomplice Junior Bradshaw.''

Sentencing on Bradshaw was adjourned until a later date.

The pair set off from their home in Manchester with a samurai sword, knives, bags and gloves crammed in their Fiat Punto, bound for Miss Stone's address in mid-Devon.

Unfortunately for the hapless pair, their plot was fraught with problems.

They were spoken to by police having been involved in a crash on the journey to the West Country from Manchester.

Bradshaw and Liverpool also asked a postman for directions to Miss Stone's home in Ashill using a picture of the pop star in an attempt to track her down.

The duo had previously gained evidence about one of Miss Stone's former homes, near Cullompton, after studying a video documentary she made for MTV's Cribs series and printed Google street maps to find her new address a short distance away.

Notes found in the defendants' possession showed they intended to decapitate the pop star before planning to dump her body in a river, the prosecution told jurors.

Bradshaw and Liverpool were arrested on the morning of June 13 2011 a few miles from Miss Stone's home when concerned local residents - spotting their crash-damaged car - called police.

Both men - who are long-standing friends and call each other ``cousins'' even though they are not related - told police they were lost and were trying to get to Bristol.

Bradshaw also told officers they had been stopped a few miles away and the vehicle had been checked before being given the all-clear to carry on their journey.

But it turned out the pair had actually been stopped at the M5 Michaelwood services in Gloucestershire at 5am that day.

They had been involved in a collision with metal railings and a digger, leaving the Punto badly damaged.

Officers from Gloucestershire Police thought the vehicle was too badly damaged to be driven and left.

Their decision allowed Bradshaw and Liverpool to continue their trip south.

They became lost around seven miles from Miss Stone's home and they showed local postman Alex Greening a map with handwritten notes on it, as well as a picture of the 25-year-old soul singer.

Bradshaw and Liverpool were quizzed on Cullompton High Street after residents called police.

The suspicious uniformed Pcs discovered Bradshaw did not have a driving licence and arrested him.

They searched the Punto and found a stash of weapons, including a black-handled samurai sword, three knives, a section of garden hosepipe, two #1 hammers, black gloves and balaclavas and a further holdall containing a metal spike, black bags and black tape. There were also print outs of AA routefinder maps from Manchester to Devon.

Liverpool was branded a fantasist by his own lawyer.

Notes he wrote found in the car and his flat in Manchester included references to robbing, killing and beheading the singer and dumping her body in a river.

Other documents also `"appear to express disapproval of the Royal family''.

One note added: "The Queen - she-devil. But she likes Joss Stone. Invited to Will's wedding by Queen. Where's the sense in that?''

A search of the one-bedroom flat Bradshaw and Liverpool shared also recovered a self-cocking crossbow and a BB gun.

Police also found in the flat Liverpool's rambling hand-written diaries, which talked of the need to buy a semi-automatic gun, a silencer, infra red sights and a "ninja'' sword.

He called Miss Stone "princess'' and other entries referred to ``Jocelyn RIP - try to get info. Rob and kill.''

Another said: "Jocelyn - devil. She devil in flesh. The Queen. She devil/her system take the p.... Destroy The Queen's system.''

His notebooks also listed other musicians such as Dizzee Rascal, Eminem, Beyonce, Craig David, R Kelly, Chris Brown and girl band Girls Aloud.

Prosecutor Simon Morgan told the court: `"This case is about a decision by a group of individuals, of which these defendants are two, to rob and kill Joss Stone.

"That is not a phrase I have plucked from the air. It is used in documents written by Mr Liverpool during the planning stages of this plot. We don't know who the others are but that does not matter.

"In interview, the defendants, in essence, declined to comment. The items in their possession, the trips to the area, the fact that the intended victim was at home, the notes and maps all point to a determined effort on the part of the defendants to carry out the plan they had hatched some time before.

"The evidence established that they intended to rob and kill their target using the equipment they had with them.''

Giving evidence to jurors, the soul star admitted there was lax security at her home but said she only learnt of the plot against her when told by police.

Miss Stone, who was referred to by her real name Jocelyn Stoker, said: "I've lived in Devon for a long time and nobody really shuts their door.

"I had an alarm but I did not really turn it on very much. I didn't really have a lock on my door... But I do now.''

During the trial Bradshaw said he had never heard of The Fell In Love With A Boy singer until his arrest and that he believed he was on a day out with his friend.

Consultant psychiatrist Dr Michael Alcock said Bradshaw suffered from disorganised schizophrenia and had such a poor concept of time that he thinks the alleged murder plot only happened two or three months ago.

"In a sense, his mental illness and learning difficulties are protecting him. Ironically, his disorder is helping him get through,'' he said.

"Each day is the same to him. He is like a goldfish in a bowl. It doesn't bother him.''

Bradshaw, who has spent time detained under the Mental Health Act in psychiatric units, also has a low IQ of between 55 and 65.

Forensic psychiatrist Dr Richard Latham, who was called to give evidence by the prosecution, said Bradshaw was well at the time of the plot.

He agreed with Dr Alcock's fundamental diagnosis but disputed the effect it had on Bradshaw at the time.

"It all points to him being in a period of remission. He was well at this stage,'' he said.

"The overwhelming evidence is that he was not in a state of relapse at that time.''

Liverpool chose not to give evidence and none was called on his behalf.

His barrister, Philip King QC, used his closing speech to say the plot to kill Miss Stone was nothing more than a bungled fantasy that was never going to be carried out.

"The simple truth is that you have one, maybe two people who are incapable, bizarre, deluded incompetents. They were doing nothing other than living out a frightening fantasy,'' he told jurors.

"It was a frightening fantasy but are you sure he intended real harm to occur in the real world.''

Mr King said the notes written by Liverpool showed how removed he was from reality, with references to acquiring machine guns, infrared sights and silencers.

He said: "He never got these things, he never got within a million miles of them. You have to consider whether these are just the lunatic ramblings of someone who was not very well.

"The sad truth is he is not dangerous, just a deluded inadequate; part of the crooked timber of humanity.

"He may just be a man who needs some sort of help. He may just be an incapable fantasist.''

Martin Meeke QC, for Bradshaw, said the medical evidence showed that his client was also incapable of taking part in any sort of plot and there was no forensic evidence to link him to either the weapons or the notes or to suggest he took part in any planning.